This invention relates to barriers for preventing ink from escaping from an ink reservoir to which a vacuum or pressure line is connected.
In many ink jet systems, an ink jet printhead contains a reservoir from which ink is supplied to pressure chambers for ejecting ink drops through an array of orifices in response to drop-ejecting signals. As the ink in the reservoir is used, air is drawn into the reservoir through a vent. Moreover, to prevent weeping of ink through the ink jet orifices to which the reservoir is connected, a small negative pressure is usually applied to the reservoir vent and, to purge contaminated ink from the ink jet orifices, a positive pressure is applied to the vent.
In certain cases, an ink jet printhead must be arranged to operate in different orientations, e.g. with the array of orifices aligned in a generally horizontal direction and ejecting drops in a generally horizontal direction, or with the array of orifices aligned in a generally vertical direction and oriented to eject drops horizontally or with the array of orifices aligned in a generally horizontal direction and oriented to eject drops vertically in the downward direction. In an ink jet printhead adapted for use in such a variety of orientations, however, care must be taken to prevent ink from flowing into the reservoir vent or the associated pressure or vacuum line not only in each of the orientations during normal use, but also when the ink jet printhead is completely inverted or shaken during handling.
In order to prevent ink from reaching a reservoir vent, the Yuki et al. U.S. Pat. No. 4,658,273 provides a labyrinth passage containing spaced barrier walls leading to a chamber from which the vent opens to the atmosphere. In the Deur et al. U.S. Pat. Nos. 5,276,468 and 5,386,224, a U-shaped air path extends between an ink reservoir and a vent for the purpose of trapping impurities in the air entering the vent before it reaches the reservoir. The Cowger et al. U.S. Pat. No. 4,931,811 shows labyrinthine spiral and U-shaped paths intended to isolate a liquid valve from the atmosphere and from an ink reservoir, respectively. In that patent the U-shaped paths have a dimension small enough that ink will form a complete meniscus across the cross-section at any location in the passage so that the portion of the passage receiving ink is completely filled with ink. Moreover, the passage is long enough so that any ink which has been drawn into the ink passage will flow back into the ink jet reservoir when the pressure in the reservoir is reduced. None of the prior art, however, discloses a reservoir arrangement for preventing ink from a reservoir to escape through a vent or vacuum or pressure line connected to the reservoir when the printhead is oriented in any of three mutually orthogonal orientations.